1. Brief Summary of the Invention
This invention relates to a method and apparatus for manufacturing corrugated fiberboard using laminated corrugating media.
FIGS. 1 and 2 illustrate the respective configurations of single-wall and multi-wall corrugated fiberboard obtained by applying the processing method and apparatus relevant to the invention. Corrugated fiberboards having the configurations depicted herein are already well known, for example, as disclosed in U.S. Pat. Nos. 3,293,107 and 1,119,146.
2. Description of the Prior Art
The manufacture of such corrugated fiberboards comprising laminated corrugating media entails numerous difficulties which prevented the particular process from being put into practical use before the year 1975.
U.S. Pat. No. 1,100,065 described a method in which an adhesive is coated onto a corrugating medium as a series of thin lines, whereby the corrugating medium is laminated with another corrugating medium. The present invention also involves a method and apparatus, whereby an adhesive is coated over the whole area of the corrugating medium so as to impart added strength upon lamination.
Relating to the method and apparatus used for coating adhesive over the whole surface of corrugating media, Japanese Pat. Nos. 60714/76 and 4690/79 were laid open to the general public in 1976 and 1979 following Application Nos. 13591/74 and 69438/77 tendered by the Applicant in 1974 and 1977, respectively. Water-soluble starch and resin-emulsion adhesives, commonly used on account of their safe handling and economical advantages, often give rise to serious problems when used to coat whole surfaces of corrugating media. Namely, corrugating media are far from being homogeneous but rather show slight localized discrepancies with respect to stock thicknesses and moisture contents. Consequently, the moisture carried by the water-soluble adhesives is selectively absorbed in various amounts, depending upon the original condition of the medium's surface. Areas containing excess moisture tend to spread out, whereas those with the right thickness and original moisture content are less affected. Outspread areas bounding less-affected ones thus create series of "high-and-lows" and produce a rugged surface which, upon processing on a conventional laminating apparatus are swollen further owing to the application of steam, thereby producing localized wrinkles.
For instance, Japanese Pat. No. 148395/78 laid open to the public in 1978 upon Application No. 64144/77 tendered by the present Inventors in 1977 describes a type of laminating apparatus, the features of which involved two corrugating media that were pasted together over a preheating cylinder and were then separated for a short while to allow evaporation of excess moisture prior to re-pasting (See FIG. 11) Although this particular system fairly well prevented the occurrence of wrinkles, localized stretching caused when the two corrugating media were peeled off, one from the other, introduced new problems. Furthermore, the deformation of one of the corrugating media induced by the guide-roller used to separate the two bonded corrugating media could not be avoided, whereby production runs higher than 90 m/minute were rather difficult to carry out.
The Japanese Pat. No. 4690/79 related to the method and apparatus described in the Application tendered in 1978 under No. 69438/78 mentioned in the foregoing, provides a further attempt to overcome the formation of wrinkles. However, the piercing of minute holes in the surface of corrugating media and liner webs in order to promote exudation of trapped moisture, brings about a certain impairment in the strength characteristics of the resulting corrugated fiberboard.